Hepatocyte growth factor (HGF), also known as scatter factor, is a multi-functional growth factor that enhances transformation and tumor development by inducing mitogenesis and cell motility. Further, HGF promotes metastasis by stimulating cell motility and invasion through various signaling pathways.
In order to produce cellular effects, HGF must bind to its receptor, c-Met, a receptor tyrosine kinase. c-Met is a widely expressed heterodimeric protein comprising of a 50 kilodalton (kDa) α-subunit and a 145 kDa β-subunit (Maggiora et al., J. Cell Physiol, 173:183-186 (1997)). The c-Met β-subunit comprises the tyrosine kinase domain and two autophosphorylation sites, Y1349 and Y1356, that are critical for transmission of the HGF signal (Maggiora et al., J. Cell Physiol, 173:183-186 (1997); Ponzetto et al., Cell, 77:2610271 (1994); Maina et al., Cell, 87:531-542 (1996)).
HGF binding to c-Met results in activation of a number of signaling pathways that result in various cellular activities associated with diseases like cancer. These include promoting mitogenesis, cell survival, cell motility, invasion of the extracellular matrix (ECM), angiogenesis and metastasis, all of which are activities that promote transformation and disease progression (Jeffers et al., J. Mol. Med., 74:505-513 (1996); Amicone et al., EMBO J., 16:495-503 (1997); Matsumoto and Nakamura, Biochem. Biophys. Res. Comm., 239: 639-644 (1997); Corps et al., Int. J. Cancer, 73:151-155 (1997)). Expression or over-expression of both HGF and c-Met can result in morphological transformation and tumorigenicity of several cell types (Jeffers et al., J. Mol. Med., 74:505-513 (1996). HGF and c-Met expression or over-expression also promote mitogenesis and anchorage independent growth (Rubin et al., Proc. Natl. Acad. Sci. USA, 88:514-419 (1991); Kan et al., Biochem. Biophys. Res. Commun., 174:331-337 (1991). In particular, invasion of the ECM has been reported when activation of c-Met causes the expression of proteases, such as urokinase-like plasminogen activator and collegenase, allowing cells to degrade and locally invade tissue (Jeffers et al., J. Mol. Med, 74:505-513 (1996). Further, several tumors that express or over-express only c-Met, and not HGF, utilize a paracrine rather than an autocrine signaling mechanism to support tumorigenesis (Beviglio et al., Int. J. Cancer, 74:301-309 (1997).
HGF and c-Met also have been implicated in the etiology of many human cancers. Concomitant expression or over-expression of HGF and c-Met has been observed in breast carcinoma (Nagy et al., Surg Oncol., 5:15-21 (1996); Tuck et al., Am. J. Pathol., 148:225-232 (1996), pancreatic carcinoma (Ebert et al., Cancer Res., 54:5775-5778 (1994), oral squamous cell carcinoma (Marshall and Kornberg, Laryngoscope, 108:1413-1417 (1998), gliomas (Koochekpour et al., Cancer Res., 57:5391-5398 (1997), and malignant pleural mesotheliomas (Tolpay et al., J. Cancer Res. Clin. Oncol., 124:291-296 (1998); Klominek et al. Intl. J. Cancer, 76:240-249 (1998)). In addition, over-production of c-Met may be important in the development of other tumors in which a role for HGF has yet to be substantiated. These cancers include hepatocellular carcinoma (Suzuki et al. Hepatology, 20:1231-1236 (1996), renal cell carcinoma (Natali et al., Intl. J. Cancer, 69:212-217 (1996), lung carcinoma (Harvey et al., J. Pathol., 180:389-394 (1996), ovarian cancer (Nagy et al., J. Surg. Oncol., 60:95-99 (1995), gastric carcinoma (Taniguchi et al., Cancer, 82:2112-2122 (1998), and colorectal carcinoma (Hiscox et al., Cancer Invest., 15:513-521 (1997). In addition, germline and somatic mutations that activate the c-Met receptor in the absence of HGF in individuals with papillary renal carcinomas have been reported (Schmidt et al., Nat. Genet., 16:68-73 (1997); Jeffers et al., Proc. Natl Acad. Sci. USA, 94:11445-11450 (1997)). Other carcinomas, including those of the stomach, rectum, lung, pancreas, breast, and bile duct have been detected in individuals with c-Met containing activating mutations (Zbar et al., J. Urol., 151:561-566 (1994).
A strategy for inhibiting c Met binding is needed to prevent activation of pathways leading to diseases such as cancer. C-Met function may attenuate c-Met activation and/or HGF-induced biological responses (Date et al., FEBS Letters, 420:1-6 (1997); (Kaji et al, Cancer Gene Ther., 3:393-404 (1996); (Li et al., Clin. Exp. Metastasis, 16:74-82 (1998)) and therefore inhibit tumor progression. Although mouse anti-c-Met monoclonal antibodies having anti-mitogenic activity in cell culture have been reported (U.S. Pat. No. 5,646,036, U.S. Pat. No. 6,207,152, U.S. Pat. No. 6,214,344), a mouse antibody cannot easily be used to treat human patients. Thus, there is a need for improved compositions that will bind c-Met, and that can be used, e.g., to inhibit HGF- and c-Met-dependent tumor growth by inhibiting mitogenesis, invasion, metastasis, and/or survival.